1. Field of Invention
The present invention relates to a variable valve device. More particularly, the present invention relates to a variable valve device that has a variable valve device for two valves operated, and that can easily sense a malfunction of the variable valve device.
2. Description of Related Art
Generally, an internal combustion engine generates power by burning fuel and air input into a combustion chamber. Intake valves are operated by a camshaft, and air is input into the combustion chamber when the intake valves are open.
Also, exhaust valves are operated by the camshaft, and the air is exhausted from the combustion chamber when the exhaust valves are open.
Optimum operation of the intake valves/exhaust valves is changed according to engine speed.
That is, an appropriate lift or an appropriate opening/closing time is changed according to the engine speed.
As described above, in order to realize an appropriate valve operation according to the engine speed, the cams driving the valves are multiply designed, or a variable valve lift (VVL) in which the valves can operate at different lifts according to the engine speed has been researched.
Also, cylinder deactivation (CDA) is a similar concept to the VVL. During CDA, some cylinders are deactivated when braking or running at a predetermined speed, and the fuel supply to the deactivated cylinders and the operation of the intake valves/exhaust valves are stopped.
The VVL apparatus and the CDA apparatus have common ground to adjust valve lifts.
As described above, the optimum intake air and intake speed are varied according to an engine condition. That is, rapid air speed is needed in a low load region, and on the other hand, much intake air is needed in a high load region.
To meet above demanded condition, variable valve lift (VVL) can be adopted in the intake valves.
In that case, the intake air moves fast in a low lift mode, and a high lift mode is applied in a high load region and much air is taken in, so performance, emissions, fuel consumption can be improved.
However, as shown in FIG. 8, which is a perspective view of the conventional VVL apparatus, if a cam 22 connected to a camshaft 20 presses a VVL apparatus 10, a valve 30 moves downward. The conventional VVL apparatus has used one VVL apparatus per valve, so two intake VVL apparatuses and two exhaust VVL apparatuses are needed per cylinder.
Because one VVL apparatus operates one valve, only when all the four valves operate normally does the VVL apparatus operate normally. In addition, sensing a malfunction is difficult during a malfunction of one valve, so considerable resources must be invested to sense the malfunction such that the cost is high. Further, the problems are accompanied if only one VVL apparatus per valve is equipped.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.